weird ambient occlusion shadow
For me it looks like a somehow artifact of Approximate method of calculating AO. If you slower Error value in Approximate settings, you will likely get rid of this effect (and increase your baking time):



(I added Edge Split modifier here)

If using Raytrace method (like it's already described here), results will be similar, but at the same time you'll have more control over settings (actually, over baking time):



.blend